1. Field of the Invention
The present invention relates to a surface coating applied to an existing surface, and more particularly, not by way of limitation, to a rut resistant coating on an existing surface and a method for applying the rut resistant coating on the existing surface to increase resistance to rutting caused by lateral movement of the pavement materials due to high shear stresses caused by traffic. In addition, the rut resistant coating of the present invention provides increased resistance to high vertical and horizontal strains caused by cracks or irregularities in the existing surface.
2. Description of the Related Art
It is desirable to place a new surface or a new pavement over existing pavement used to construct roads, parking lots, airport runways, airport taxiways, and the like and not have existing cracks reappear in the new pavement for long periods of time. Cracks in the existing pavement are a form of distress, which can lead to premature failure of the new pavement. The cracks allow moisture (i.e. water) to enter into the existing (i.e. underlying) pavement and create structural support issues. Additionally, the cracks can also create ride quality issues, which may require grinding to smoothing, time intensive crack filing operations to seal the pavement, or significant costs to apply one or more additional pavement layers to address the problem.
It is common for pavements to crack during their expected service life. Reflective cracks occur when a pavement layer is placed over an existing cracked pavement. The existing cracks transmit into the new pavement after a period of time. These cracks in the new pavement can be created by several mechanisms, one of which is thermal stress. The pavement cracks form when asphalt in the pavement hardens from aging to the point that it cannot relieve the stress as the pavement tries to bend from the differences in temperature from the top of the pavement to the bottom of the pavement. Thermal cracks normally manifest as cracks that run transverse to the direction of travel.
Heavy truck loading also causes cracks in the pavement. Radial tires of trucks used in the heavy truck loading impart a tensile force at the outer edge of the radial tires on the surface of the pavement. This tensile force can create a longitudinal crack where the outer edge of the radial tires contacts the pavement. Construction issues may also contribute to longitudinal cracking. Segregation of a pavement mixture may occur from mechanical issues with the paving equipment. The segregation occurs during placement of the material and runs in a direction of the paving equipment.
Generally, the lesser the thickness of the new pavement, the lesser the time before the crack becomes visible in the new pavement. To those skilled in the art, a general rule is that every inch of new pavement provides about one year delay in reflective cracking (i.e. a crack in the existing pavement propagates a crack in the new pavement wherein the crack in the pavement will grow about one inch per year). The generally accepted practice to combat the “one (1) inch per year” crack propagation is to place four (4) inches or more of paving mixture on existing cracked concrete or pavement to keep cracks from appearing for several years. This is an inefficient solution to the problem because of the increased cost and time to lay the paving mixture in amounts that large.
Interlayer type materials are a method of addressing reflective cracking. There are different methods and materials used for constructing an interlayer. One method for constructing an interlayer utilizes applying a heavy application of a liquid binding material followed by an application of an aggregate. This technique was once thought to be limited by the amount of liquid binding material that may be applied without creating flow of the liquid binding material to areas other than intended. It was also once thought that only larger aggregate sizes can be used so as to permit the heavy application of liquid binding material.
Another form of interlayer may involve the placement of a fabric or grid material in a layer of a liquid binding material. The grids or fabrics are challenging to place smoothly, especially when paving is not in a straight line. Grids and fabrics are not intended as a surface for normal traffic. Therefore, grids and fabrics must be covered with a suitable surface material before normal traffic can be resumed. In addition, grids and fabrics are extremely expensive and are relatively slow to construct
An alternate form of interlayer may be in the form of an asphalt-aggregate mixture. This technique utilizes high asphalt content in the paving mixture, usually of a highly elastic nature. It was once believed that high asphalt content pavement poses the problem of the liquid binding material flowing from the mixture during manufacture or placement. It was once thought that high asphalt content interlayer mixtures may be sensitive to deformation from traffic and may provide low texture, reduced safety for the motoring public, and/or rutting. Therefore, it is covered with a suitable surface material as soon as possible. In all cases, the interlayer material or process is followed with at least one additional layer of paving material. An example of this type of a suitable surface coating is shown in U.S. Pat. No. 5,069,578, issued to Bense et al. (the Bense et al. patent) on Dec. 3, 1991. The Bense et al. patent provides a relatively thin pavement having a higher asphalt content than was known by those of ordinary skill in the art at the time. One problem with the pavement disclosed in the Bense et al. patent is that the pavement readily cracks in less than about one (1) year. It was once believed that the Bense et al. patent provided the upper limit as to how much asphalt could be used in the pavement and still maintain the stability of the pavement and resist rutting. One factor in the rutting of pavements was believed to be caused by over saturation of the aggregate particles with binding material. It has since come into question where the point of over saturation occurs.
An aggregate material (hot mix asphalt) has a varying percentage of air voids when applied in paving applications. When the aggregate material is used in paving applications with asphalt material, the asphalt material fills a percentage of the air voids present in the aggregate material. In the past, it was believed that about 5% of the air voids of the aggregate material need to remain unfilled to maintain the necessary structure of the pavement and resist rutting.
Accordingly, there remains a need for a method to efficiently create a surface coating having crack and rut resistant properties wherein the crack and rut resistant properties are enhanced to extend the life of the surface coating prior to cracking of the surface while still maintaining stability of the surface coating to allow the safe travel of traffic.